Centrifugal fans are used in many different industries to generate pressurized flow or vacuum to perform myriad functions. Centrifugal fans have a number of advantages over positive-displacement blowers, which makes them preferable for certain applications.
Centrifugal fans are widely used in the agricultural industry and are incorporated to perform a range of functions relating to: a) planting crops; b) harvesting crops; c) treating crops as through the application of fertilizer and other additives; d) handling crops; e) handling agricultural debris; f) preparing ground for planting of crops, etc. Regardless of their specific function, the centrifugal fans in the agricultural environment are commonly exposed to extreme conditions. The air that is handled by the centrifugal fans generally has abrasive particulate entrained therein, be it from the soil, crops, crop debris, soil and crop treating additives, etc.
Heretofore, centrifugal fan rotors have been made with a relatively lightweight blade construction based upon considerations of economy, efficiency of operation, etc. Rotors with blades made from relatively light gauge metal sheet material are common.
Thin blades on fan rotors are prone to wearing quickly in the agricultural environment. In a typical harvesting operation that utilizes a centrifugal fan to perform one or multiple functions in association with harvesting equipment, potentially large volumes of small particulate and even larger foreign matter may be passed into and out of the fan. A large percentage of this foreign matter may directly contact the rotor blades responsible for high volume air handling. Typically encountered chaff, dust, debris, etc. has the capability of wearing blades, made even from steel, to the point that they fail in potentially a single day's activity. For example, some constructions may be such that the steel blades may have to be replaced after harvesting crop in a 200-300 acre field. Blades made from other, softer materials, such as aluminum, would be expected to wear even more quickly and extensively.
One potential solution to the abrasive wear problem is to make the blades from a thicker material. This in turn necessitates a larger drive capability which puts additional strain on the power source, which is typically a power take-off on a vehicle which is responsible for advancing the various agricultural equipment throughout a field.
In the event of a failure of one or more blades on a centrifugal fan rotor, operations may need to be halted to allow the defective rotor(s) to be repaired or replaced. In a harvest season with shortened daylight hours, and potentially many days with inclement weather that make harvesting impractical or impossible, minimizing downtime is critical to profitability.
Furthermore, blade failure on rotors turning at high speeds could inflict damage on the surrounding housing, the turning shaft, and potentially other equipment parts on or in the vicinity of the fan structure.
Users of centrifugal fans in any environment wherein abrasive is entrained in the handled air are always seeking designs of rotors that maximize the often competing objectives of reducing weight, reducing down time, increasing durability and extending system life, and ensuring affordability.
For example, while a welded structure may have excellent strength and durability, the welding process can be relatively expensive, particularly with a design requiring separate welding of each of multiple blades.
Some designs rely upon strategic blade bending to effect securement. This type of construction generally limits the gauge of the material from which the blades can be formed. Heavy gauge materials may be prone to failure upon being bent in certain ways. While lighter gauge materials reduce weight, the blades formed therefrom may be more prone to detrimental wear in normal use.